Cosmic evolution of quasar clustering: implications for the host haloes

We present detailed clustering measurements from the 2dF Quasi‐Stellar Object Redshift Survey (2QZ) in the redshift range 0.8 < z < 2.1 . Using a flux‐limited sample of ∼14 000 objects with effective redshift z eff = 1.47 , we estimate the quasar projected correlation function for separations 1 < r / h −1   Mpc < 20 . We find that the two‐point correlation function in real space is well approximated by a power law with slope γ= 1.5 ± 0.2 and comoving correlation length r 0 = 4.8 +0.9 −1.5   h −1 Mpc . Splitting the sample into three subsets based on redshift, we find evidence for an increase of the clustering amplitude with look‐back time. For a fixed γ, evolution of r 0 is detected at the 3.6σ confidence level. The ratio between the quasar correlation function and the mass autocorrelation function (derived adopting the concordance cosmological model) is found to be scale‐independent. For a linear mass‐clustering amplitude σ 8 = 0.8 , the ‘bias parameter’ decreases from b ≃ 3.9 at z eff = 1.89 to b ≃ 1.8 at z eff = 1.06 . From the observed abundance and clustering, we infer how quasars populate dark matter haloes of different masses. We find that 2QZ quasars sit in haloes with M > 10 12 M ⊙ and that the characteristic mass of their host haloes is of the order of 10 13 M ⊙ . The observed clustering is consistent with assuming that the locally observed correlation between black hole mass and host galaxy circular velocity is still valid at z > 1 . From the fraction of haloes which contain active quasars, we infer that the characteristic quasar lifetime is t Q ∼ a few × 10 7 yr at z ∼ 1 and approaches 10 8 yr at higher redshifts.